<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>

    <link href="http://apps.bdimg.com/libs/bootstrap/3.3.4/css/bootstrap.min.css" rel="stylesheet">
    <script src="http://apps.bdimg.com/libs/jquery/2.1.4/jquery.min.js"></script>
    <script src="http://apps.bdimg.com/libs/bootstrap/3.3.4/js/bootstrap.min.js"></script>
    <!--[if lt IE 9]>
    <script src="https://oss.maxcdn.com/libs/html5shiv/3.7.0/html5shiv.js"></script>
    <script src="https://oss.maxcdn.com/libs/respond.js/1.3.0/respond.min.js"></script>
    <![endif]-->

    <style>
        .main {
            display: flex;
            flex-direction: row;
            justify-content: space-around;
            align-items: center;
        }

        .content {
            width: 90%;
            height: 1000px;
            background-color: #2a6496;
        }

        .left-menu {
            position: fixed;
            top: 0;
            left: 0;
            width: 45px;
            height: 800px;
            background-color: #2A2A2A;
        }
    </style>
</head>
<body>
<div class="main">
    <div id="left-menu" class="left-menu">
        <a id="left-menu-btn" href="#" class="list-group-item"
           style="border-radius: 0;border:0;background-color: #5bc0de">
            <span class="glyphicon glyphicon-th-list" style="color:white;"></span>
        </a>
    </div>
    <div class="content">

    </div>
</div>
</body>
<script>
    var isClick = false;
    $('#left-menu-btn').click(function ()
    {
        var left_menu = $('#left-menu');
        if (!isClick)
        {
            left_menu.animate({
                width: 300
            });
            isClick = true;
        }
        else
        {
            left_menu.animate({
                width: 45
            });
            isClick = false;
        }
    });
</script>
</html>